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InCITE 2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 273 2017 012023 doi:10.10881757-899X2731012023
were also easily detached from the interface thus destabilization occurred. Silica particles were difficult to be adsorbed in the interface of oil-water, but once being adsorbed; they stayed and
stabilized the system [5]. Therefore, mixtures of amphiphilic polymer and solid particles were used to have a synergism effect [6]. Polymeric emulsifier was attached on the surrounding surface of oil-water
interface while reducing the surface tension between two phases and solid particle formed the barrier on the oil globule surfaces thus preventing recoalescence which would lead to oil globule separation
[6]. Emulsifier mixtures could reduce the rate of ow emulsion destabilization.
Coalescence is the merging of smaller oil globules into bigger ones. In general, coalescence process which leads to ow emulsion destabilization followed the first order kinetic model [7]. By
investigating the kinetics of emulsion destabilization, the effect of mixed emulsifiers’ concentrations on the emulsion stability could be well investigated. This research was expected to give the beneficial
contribution to the food industries dealing with development of a more healthful food emulsions for the determination of product shelf-life and storage condition. The aim of this research is to study the
stabilization of ow emulsion using mixture of various concentration of Tween-20 combined with rice husk silica for the formulation of food grade ow emulsion with kinetics approach.
2. Materials and methods
2.1 Materials Tween-20 Merck, Germany; rice husk derived from Mojokerto, East Java, Indonesia; palm oil
consisting of 40 saturated fatty acid mainly palmitic acid and 60 unsaturated fatty acid mainly oleic acid with FFA content of less than 0.3 SunCo, PT. Milkie Oleo Nabati Industri, Bekasi,
Indonesia; and demineralized water. 2.2
Preparation of rice husk silica Clean and dried rice husks were leached out using citric acid 5 in an agitated flask for the metallic
impurities removal. Afterwards, they were rinsed several times using demineralized water and then dried in an oven Memmert, Germany at 105
o
C for 2 hours. Leached dried rice husks were then thermally treated in a furnace Ney VULCAN D-550, Dentsply Ceramco, USA
at 750
o
C for 5 hours. White ashes consisting of almost pure silica 95 were obtained after the thermal process. The rice
husk silica were milled and screened. Biosilica of 200 mesh were used as the emulsifier of ow emulsions. Biosilica is amorphous and inherently nanostructured with primary spherical particle of
several nm in diameter [4]. 2.3
Preparation of ow emulsion stabilized with tween-20 and rice husk silica mixtures. Aqueous phase was prepared by adding biosilica 2.5 and Tween-20 0.1-1 into the
demineralized water and then mixed using a magnetic bar and heated to 50
o
C for 15 minutes. Oil was poured into a beaker glass and heated up to 50
o
C for 15 minutes. Oil of 20 was then added into the aqueous phase and emulsified for 5 minutes using a rotor-stator homogenizer IKA T25 digital
ULTRA TURRAX, Germany at 20,000 rpm. The pH of the emulsion was not adjusted. The resulting ow emulsion was quickly quenched in an ice bath for about 15 seconds. Some emulsions were
prepared without any emulsifiers, with Tween 1 only, and with biosilica 2.5 only as controls. The emulsions were transferred into transparent 40 ml glass vials ID= 25 mm, height= 95 mm until
reaching the height of ~ 4 cm from the bottom and then stored at a room temperature of ~ 28
o
C for stability tests.
2.4 Determination of emulsion stability
The height of emulsion was measured every 1 minute for the first ten minutes, followed by the measurement in every 5 minutes afterwards until the first one hour, and then the measurement was
taken in every 10 minutes for the next one hour. The stable emulsion layer was indicated by a milky
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InCITE 2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 273 2017 012023 doi:10.10881757-899X2731012023
appearance with the formation of neither cream nor silica particles sediment. The emulsion stability S was calculated by using equation 1.
100 x
h h
S
t
1
Whereas
t
h is emulsion height at a certain time and h is initial emulsion height.
2.5 Determination of kinetic models of destabilization rate of ow emulsion.
The data used for the kinetic models determination was within 0-120 minutes, since the emulsion stability remained more or less constant after 120 minutes. The destabilization rate of ow emulsion
was fitted using the zero order or first order kinetic models. The most appropriate kinetic order would be chosen based on the best obtained correlation coefficient R
2
calculated using the least square procedure. The destabilization rate of the emulsion could be written in an equation as follows [8]:
a
S k
= dt
dS =
r
2
t k
S =
S
3 t
k lnS
= lnS
1
4
with
dt dS
the rate of emulsion destabilization, a the order of emulsion destabilization rate,
k
and
1
k the emulsion destabilization rate constants for the zero order stability minute and for the first
order per minute, respectively, t the storage time minute, the percentage of emulsion stability
after time t and
S
the initial emulsion stability percentage.
3. Results and discussion
